1. Field of the Invention
The invention relates generally to the field of integrated circuit design and manufacturing. More specifically, the invention relates to systems for testing integrated circuit designs and chips from a location remote from physical testing equipment.
2. Description of the Related Art
Because of increasing complexity of newly developed integrated circuits, new types of integrated circuit manufacturing techniques have been developed. Currently, integrated circuit manufacturers commonly use one of several possible approaches to make their products. First, a manufacturer can build and run its own factories to make the semiconductors themselves. These factories are known as semiconductor foundries or fabrication plants. Some companies only operate such fabrication plants, leaving other steps in the development of new integrated circuits to others. A number of large companies, known as “integrated device manufacturers” (IDMs) have both the ability to design and test new semiconductors. IDMs also own their own fabrication plants. Alternatively, a company can restrict itself to designing integrated circuits that ultimately are then produced by another. Traditionally, it was common for a manufacturer to be an IDM. A number of fabrication plants, or “fabs”, were built by such IDMs. In order to save capital and operating expenses, the owners of “fabs” sometimes built plants in lower-cost countries. Typically, however, the “fabs” themselves possessed very little capability for semiconductor design. As a result, some companies have begun to appear whose sole concern is to design integrated circuits. These design companies, which may have no manufacturing or testing capability, typically contract out the testing and production of integrated circuits to others. Many smaller companies often have no capabilities beyond the initial design of integrated circuits. All the intermediate steps between initial design and production are contracted out to third parties. These design-only companies are referred to as “fabless” firms. Fabless firms generally have a need for testing services to be provided by third parties. However, the fabless firm also has a need to remain closely involved with testing steps that take place prior to “hand off” of the integrated circuit design to volume manufacturing due to the fact that the circuit design may undergo a number of changes during the development process.
There are many intermediate steps between the conceptual development and the actual volume production of a new integrated circuit. The first step in bringing a new design to the production stage is the initial design. In the initial design, a design engineer, using an end user's specifications, develops a series of logical gates that the design engineer believes will produce the end user's specified functionality in a completed integrated circuit. At this stage, the design engineer produces only an arrangement of logical elements, and typically does not physically construct any device.
The next step is testing the initial design to determine if the integrated circuit will produce the user's specified functionality. At this stage, the testing generally involves simulating the arrangement of logic gates on a computer, and determining the actual functionality of the logic gates so arranged. Changes to the arrangement of logic gates can be performed on the simulation computer to rectify any deficiency in producing the user's specified functionality. The testing and design is then repeated until the logical design meets the user's desired specifications. This re-testing and re-designing cycle is known as debugging. Debugging typically only includes rearranging the simulated or theoretical gates to produce the desired functionality. The testing, at this stage, is typically not rigorous and serves only to confirm that the logic gates are arranged in a proper fashion.
The next step of the integrated circuit development process is fabricating prototype devices, this being referred to in the art as “first silicon”. This prototype device is then tested, typically more rigorously than the simulated device, in a next step known as design debug. Because of the difficulties in reproducing a theoretical series of logic gates in three-dimensions on a silicon wafer, errors commonly arise in making first the prototype device. For example, the timing of two signals to a particular gate may be such that the desired data does not pass through the gate as expected. Therefore, the next step in the development process is to debug and possibly repair the prototype device. In order to repair the prototype device, the individual gates are evaluated and repaired as necessary to produce the end user's functionality. The gates in the prototype device are physically observed and/or repaired, by using instruments such as an “electron beam” (e-beam) probe system, an “infrared laser” (optical) probe system or a “focused ion beam” (FIB) probe system. One such e-beam machine is known by model number IDS 10000da. One such infrared laser probe system is known by model number IDS 2000. One such focused ion beam probe system is known by model number IDS P3X. All of the preceding instruments are sold by Schlumberger Semiconductor Solutions, San Jose, Calif. To repair a gate that is inoperative or not working as planned, the FIB machine can literally “burn” a hole into the prototype device, for example, cutting a wire leading to an inoperative gate. After the inoperative gate is disconnected, a new element, such as a jumper, can be put in place by the FIB probe system. After all the repairs have been made, the prototype device is re-tested until the logical elements produce the end user's desired functionality.
The next step in the process is characterization of the prototype device. The characterization step generally includes a full-scale performance test of the device. The performance test includes, for example, a determination of the actual maximum operating speed, the voltages at inputs and outputs, timing parameters and temperature limitations. If the prototype device passes the characterization test it can be “handed off” to a fabrication plant for volume manufacturing. Once the device design is delivered to the fabrication plant, test programs must be designed to test the product produced by the fabrication plant. Because every circuit design has different user specifications and different internal logical elements, new test programs must be developed for each design of device produced. The typical fabless firm may specify the test program, or the fabless firm may leave the development and implementation of test programs, either during design debug, characterization, or volume manufacturing testing to an outside company.
“Test houses” exist in the industry whose sole functions are to develop test programs and/or to perform the actual testing at the various stages of integrated circuit development. Some fabrication plants will carry out the physical testing but will not develop the test program (which may include software, test interfaces, etc.), relying instead on a test house or other entity to design the test program. The testing is carried out for the duration of the production cycle of any particular circuit design. At this point, an integrated circuit is generally ready to be sold to end users.
FIG. 1 shows a typical method that a fabless firm, for example, uses to develop a new integrated circuit from an initial design to an end product. A fabless firm 20 first designs 1 the logical arrangement of circuit elements in a proposed integrated circuit. The fabless firm 20 will simulate 2 the integrated circuit to determine whether it will function as intended. Any changes to the design 1 determined to be necessary during simulation 2 are included in the design 1 at this time. Next, the fabless firm 20 will generate a layout 3 for the integrated circuit. The completion of the layout is known in the art as “tape out”. The layout is sent to the fabrication plant 30 where a prototype will be fabricated 4. The fabrication plant 30 may itself then either debug 5A and characterize 7B the prototype or may send the prototype out for debug 5A and characterization 7B to a test house 40. Based on test results obtained during design debug 5A the fabrication plant 30 or test host 40 may modify the design 7A or a new prototype may have to be created. After determining that the prototype functions as intended, volume manufacturing of the integrated circuit can begin. Test and assembly 5B of the product made by the fabrication plant 30 may be performed by the test house 40, and the results of those tests are communicated to the fabless manufacturer 20 and the fabrication plant 30 to remedy any design and/or production flaws found during volume manufacture. Finally, the completed integrated circuits can be shipped 6 to the end user.
Because of all of the steps involved in bringing a new integrated circuit design to market, i.e., design step, repair/debug steps, and testing step, producing a new integrated circuit is difficult and expensive. Monitoring the development of the integrated circuit throughout the various stages is also a difficult task, particularly for the fabless firm who must generally contract testing to third parties.
Monitoring involves reviewing and analyzing test results and test data as they become available. For example, a fabless firm would be interested in viewing the test results on integrated circuit performance to determine if any design changes are needed, and the effect of any such design changes. Because monitoring is difficult, preventable errors in design, assembly, or other stages may not be avoided. Additionally, a fabless firm may wish to run a test program itself to speed up the review of test data, but may not have the required resources. In such a case, a fabless firm may be forced to either outsource the testing or to use the facilities of a test house.